Add Desktop GUI icon for macOS

[jacebrowning]

https://github.com/jacebrowning/doorstop/blob/2d7511ab46b40295c0cbe616195ca4de6504f447/doorstop/gui/main.py#L117-L119

See this comment for instructions: https://github.com/jacebrowning/doorstop/pull/290#discussion_r175652899

[JustinW80]

Based on this comment in #290, I made an .icns file using the CreateICNS.src script in this Stack Overflow answer to convert logo-black-white.png to logo-back-white.icns:

IFS='.' read -ra ADDR <<< "$1"
ICONSET=${ADDR[0]}.iconset
mkdir $ICONSET
sips -z 16 16     $1 --out $ICONSET/icon_16x16.png
sips -z 32 32     $1 --out $ICONSET/icon_16x16@2x.png
sips -z 32 32     $1 --out $ICONSET/icon_32x32.png
sips -z 64 64     $1 --out $ICONSET/icon_32x32@2x.png
sips -z 128 128   $1 --out $ICONSET/icon_128x128.png
sips -z 256 256   $1 --out $ICONSET/icon_128x128@2x.png
sips -z 256 256   $1 --out $ICONSET/icon_256x256.png
sips -z 512 512   $1 --out $ICONSET/icon_256x256@2x.png
sips -z 512 512   $1 --out $ICONSET/icon_512x512.png
cp $1 $ICONSET/icon_512x512@2x.png
iconutil -c icns $ICONSET
rm -R $ICONSET

Then in Terminal, enter: source CreateICNS.src . logo-black-white.png

I converted it to Base64, but now I'm having trouble getting the icon to actually show up in the GUI or Dock on macOS.

Here is my commit with my changes so far.

If someone has experience in tkinter on macOS, I could use the help!

Here are two more Stack Overflow references I researched:

• Set tkinter icon on Mac OS
• set window icon tkinter macosx

Also, maybe macOS needs iconphoto instead of iconbitmap, according to this doc to Tk commands.